The present invention relates to a bearing seal for a water pump that is suitable for an application such as a water-cooled engine of an automobile and, in particular, to a bearing seal that prevents the intrusion of water, water steam, or the like into a bearing that supports a rotary shaft of a water pump, and which simultaneously prevents any leakage of grease from within the bearing to the outside.
As shown in FIG. 6, a water pump 30 that pressurizes cooling water housed in a pump chamber 50 of an engine to cause it to circulate is generally configured in such a manner that a rotary shaft 12, on which an impeller 32 is fixed at one end and a drive means 60 comprising a pulley 61 and a drive belt 62 are fixed at the another end, is supported within a casing 38 by a plurality set of roller bearings 10 disposed having a distance therebetween in the axial direction. The cooling water is sealed from the exterior by a mechanical seal 40 that is disposed between the impeller 32 and the rolling bearings 10. However, since the sliding surface between the inner surface of the mechanical seal 40 and the rotary shaft 12 is in a water-lubricated state, water steam or the like will leak therefrom and will enter the roller bearings 10 side from the sliding surface if no further contrivance is provided. If steam or the like enters the interior of the roller bearings 10, it will damage the roller bearings 10. To prevent the intrusion of water steam or the like from the impeller 32 side into the roller bearings 10 in such a configuration, an annular seal body (not shown)is provided on the impeller 32 side of the roller bearings 10. Nitrile rubber, which has an excellent water resistance, or a fluororubber, which has an excellent thermal resistance, is used as the material of this annular seal body.
Concomitant with recent increases in engine capacities and outputs, temperature conditions for the surrounding of an engine have become more severe, so that the ambient temperature of such bearings can easily exceed 110xc2x0 C.
However, the thermal resistance of nitrile rubber reaches a limit at approximately 100xc2x0 C. Thus, if nitrile rubber is used as the material of a seal body for the bearings 10, thermal deterioration of the seal body will result in cracking and a loss of elasticity of lip portions thereof, so that the sealing properties of the seal body will be lost.
The thermal resistance of fluororubber reaches a limit at a temperature of at least 200xc2x0 C., so there would be no problem concerning thermal resistance if fluororubber were used under the above temperature conditions, but it is extremely expensive.
There is a further problem with both nitrile rubber and fluororubber in that they will deteriorate and deform if brought into contact with the additives comprises within cooling water, which would damage the sealing properties thereof.
An object of the present invention is to solve the above described problems and provide a bearing seal device for a water pump which is provided with a seal body that can be used in a high-temperature environment, does not deform when in contact with cooling water, and is also inexpensive.
The present invention achieves the above objective by providing a bearing seal for a water pump disposed within a casing, wherein the bearing seal comprises:
an outer ring formed within the casing;
a rotary shaft which is equipped with a drive portion at one end portion and an impeller at another end portion, and which is provided in a freely rotatable manner within the outer ring with rolling elements therebetween; and
a seal body affixed to each end of the outer ring in the axial direction;
wherein at least the seal body on a side close to the impeller is formed of hydrogenated nitrile rubber.
In this case, hydrogenated nitrile rubber has superior thermal and chemical resistance in comparison with nitrile rubber, and it also has a superior chemical resistance in comparison with fluororubber. If hydrogenated nitrile rubber is used as a seal body in a bearing for a water pump, therefore, the seal body can be expected to exhibit favorable sealing properties over a long period of time, without deteriorating when used in a high-temperature environment and in contact with cooling water. Thus there is no intrusion of water steam or the like into the bearing, and the bearing efficiency thereof does not deteriorate.